CRISPR/Cas9 screening identifies SUV39H2 as a key regulator of oHSV-1 resistance in oral squamous cell carcinoma.

Oncolytic viruses represent an innovative strategy for cancer therapy. However, extensive gene expression reprogramming within tumor cells may hinder viral propagation by affecting essential cell-virus interactions. Here, through genome-wide CRISPR/Cas9 library screening, Suppressor of variegation 3-9 homolog 2 (SUV39H2), a histone methyltransferase, was identified as a critical factor in mediating resistance to oncolytic herpes simplex virus 1 (oHSV-1) in oral squamous cell carcinoma (OSCC). Functional studies in SCC15 cells revealed that SUV39H2 knockdown facilitated viral replication, while its overexpression suppressed it. The inhibitor OTS186935 targeting SUV39H2 was administered to evaluate its effects on viral replication both in vitro and in vivo. Pretreatment with OTS186935 in SCC15, SCC7, and MCF7 led to a significant enhancement of viral replication. Combined treatment with OTS186935 and oHSV-1 demonstrated significant anti-tumor efficacy in BALB/c nude mice bearing SCC15 tumors. SUV39H2 was shown to regulate the trimethylation of lysine 9 on histone 3 (H3K9me3) at the viral promoter regions of immediate-early gene ICP0, ICP4 and early gene ICP8, thereby repressed viral gene transcription. However, oHSV-1 infection induced the degradation of SUV39H2, a process mediated by the viral protein ICP0 through the proteasomal pathway. Findings from studies in SCC7 cells further supported the observation that SUV39H2 knockdown enhanced viral replication. Moreover, SUV39H2 downregulation increased CD4+ and CD8+ T cell infiltration in syngeneic tumors treated with oHSV-1. TCGA database analysis revealed that SUV39H2 is associated with distinct immune cell infiltration patterns across different cancer types and correlates with immune checkpoint expression. These results highlight the role of SUV39H2 in regulating oHSV-1 replication and indicate that SUV39H2 may represent a potential target to improve the efficacy of oncolytic virotherapy.